Hydrology

• Hydrology is the science of water, dealing with the occurrence, circulation, and distribution of water on Earth and in the earth's atmosphere
• Hydrology is concerned with water in streams and lakes, rainfall and snowfall, snow and ice on land, and water below the earth's surface in soil and rocks
• Hydrology is an interdisciplinary subject drawing support from allied sciences such as meteorology, geology, statistics, chemistry, physics, and fluid mechanics
• The US National Research Council defines hydrology as the science that treats the waters of the Earth, their occurrence, circulation, distribution, chemical and physical properties, and their interaction with the environment, including living things
• Hydrology is classified as scientific hydrology, focusing on academic aspects, and engineering or applied hydrology, focusing on engineering applications
• Engineering Hydrology deals with the estimation of water resources, processes like precipitation, runoff, evapotranspiration, and their interaction, as well as problems like floods and droughts with strategies to combat them
• Periods of Hydrology by VEN TE CHOW:

  • Period of Speculation (Prior to AD 1400)
  • Period of Observation (1400-1600)
  • Period of Measurement (1600-1700)
  • Period of Experimentation (1700-1800)
  • Period of Modernization (1800-1900)
  • Period of Empiricism (1900-1930)
  • Period of Rationalization (1930-1950)
  • Period of Theorization (1950-to-date)
• Importance of Engineering Hydrology:

  • Hydrology is crucial for designing and operating water-resources engineering projects like irrigation, water supply, flood control, water power/hydropower, and inland navigation/waterways
  • It helps in determining maximum probable floods, water yield from a basin, ground water development, storm intensity, and frequency for drainage project design
• Hydrologic Cycle:

  • Water occurs in liquid, solid, and gas forms on Earth
  • The water cycle, also known as the hydrological cycle, involves processes like evaporation, condensation, precipitation, and collection of water
• Components of Hydrologic Cycle:

  • Evaporation: water evaporates from oceans and land surfaces to the atmosphere
  • Precipitation: water vapor condenses and falls back to Earth as rain, snow, or hail
  • Condensation: transition from vapor to liquid state
  • Infiltration: water enters the soil from the ground surface
  • Percolation: slow water movement through soil and permeable rock
  • Surface outflow: overflow of precipitated water from reservoirs
  • Subsurface flow: rapid flow below the surface toward stream channels
  • Surface runoff: water flowing downhill over land surface
• • Groundwater flow: movement of water underground
  • Groundwater outflow/discharge: groundwater exiting the ground